by Chris Chase, USA TODAY Sports

by Chris Chase, USA TODAY Sports

Andy Roddick moved up two spots in the ATP rankings this week, which wouldn't be noteworthy if Andy Roddick were still playing tennis.

But Roddick hasn't played a match since retiring after the U.S. Open in September. How could he go from No. 42 to No. 40 in rankings released Monday?

Short story: The ATP rankings are confusing.

Longer story: Rankings work on a rolling 52-week slate. Points are gained at tournaments, are reflected in the rankings for a year, then get dropped in the corresponding time period 52 weeks later.

For instance, once Wimbledon starts in 2013, a player's points from last year's Wimbledon get erased. If you exit at the same point in the tournament, your total would stay the same. Exit earlier, your points drop. Exit later - you get the idea.

The same thing is happening to other players, so week-to-week rankings changes essentially become a question of who can defend their rankings points from last year with better success.

Because he's not playing, Roddick's point total declines every week he drops another tournament. He held steady at 970 last week because he had no points to defend from the same week in 2012. Two other players - Viktor Troicki and Nikolay Davydenko - failed to defend their points from last year, so they fell below Roddick's point total.

This happens more often than you'd think. Serena Williams once moved back into the top 10 while out with an injury. It's a strange quirk in a strange rankings system, but it's not even the weirdest one of the week: On the women's side, Victoria Azarenka lost her No. 1 ranking to Williams despite beating Serena in the finals of the Qatar Open.

Therein lies the key issue with tennis rankings: If you're defending a title, as Azarenka was, you can't gain any rankings point that week. You can only lose them. Any points Serena earned in Doha were a net gain. Azarenka was looking at a net loss unless she won the title. At worst, Serena was chasing a stationary target. When she won her quarterfinal match, the bloodless coup was complete.

Back to Roddick, a better question about his rankings jump is why he's on the list at all. A player who submits official retirement papers falls out of the rankings. (Kim Clijsters retired after the U.S. Open, too, and she's nowhere to be found on the WTA side.) As of the release of this week's rankings, Roddick hasn't filed the paperwork yet. As a result, he'd have kept a spot on the rankings until his final tournament comes off the books. He'll likely stay in the top 50 until the week before Wimbledon. When he falls off after the U.S. Open, he'll be closer to No. 250.

That seems to be the standard procedure among men's players. Juan Carlos Ferrero, the 2003 French Open champion, left the sport in 2012 and is also still on the rankings, too. Pete Sampras and Andre Agassi let their rankings drop for the year after retirement, too.

Lest you think Roddick was keeping a return in the back of his mind, word came Tuesday that he has officially filed his paperwork. The ATP World Tour Player Relations department said Roddick will be off the rankings next week. That's bad news for lovers of comebacks, but good news for players like Troicki and Davydenko, who couldn't find a way past a player who hasn't been a player since Labor Day.